A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a light source that emits light energy for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical transformations can take place as the wafer is fabricated into a device. During rapid thermal processing, which is one type of processing, semiconductor wafers are typically heated by an array of lights to temperatures, for instance, from about 100.degree. C. to about 1,200.degree. C., for times which are typically less than a few minutes. During these processes, one main goal is to heat the wafers as uniformly as possible.
Besides heating semiconductor wafers, thermal processing chambers are also used to chemically react the wafers with other components contained within the chamber such as gases. For instance, various gases can be circulated through the thermal processing chamber which react with the surface of the semiconductor wafer during heating to form a desired film or coating on the wafer. For example, in one embodiment, steam can be present within the chamber for forming oxidation coatings on the wafer.
For monitoring the temperature of the semiconductor wafer during heat treatment and other processes, thermal processing chambers typically include radiation sensing devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected wavelength. For instance, a thermal processing chamber can contain a single pyrometer or a plurality of pyrometers which sense radiation being emitted by a wafer either at a single location or at multiple locations. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated using, for instance, Planck's Law.
In the past, however, problems have been experienced in determining the temperature of semiconductor wafers contained in thermal processing chambers using pyrometers when the processing chambers contain radiation absorbing gases, such as steam. In particular, the gases can absorb some of the thermal radiation being emitted by the wafer before the thermal radiation can be detected by the pyrometer. Thus, the amount of thermal radiation sensed by the pyrometer is less than the actual amount being emitted by the wafer, which leads to inaccurate temperature readings.
As such, a need currently exists for a process for determining the temperature of a semiconductor wafer in a thermal processing chamber when radiation absorbing gases are present within the chamber. In particular, a need exists for a system for determining the temperature of wafers in thermal processing chambers using pyrometers, when gases such as steam are present. Precise temperature determinations in thermal processing chambers are especially necessary due to the increasing demands that are being placed upon the preciseness at which the semiconductor wafers are heat treated and at which the semiconductor devices are fabricated.